Carbon Dioxide/ AGM Examples Flashcards
Review the reaction process with carbon dioxide with soda lime.
When is the soda lime absorber most efficient?
Soda lime absorbs most efficiently when the moisture content is between 10-20%
Why is moisture essential for Carbon Dioxide Absorption?
Moisture is essential because the reactions take place between ions that exist only in the presence of water
What is true about carbon dioxide absorbents with low moisture content?
Absorbents with low moisture content exhaust rapidly
What can be added to increase the speed of Carbon Dioxide Absorption?
Activators (NaOH, KOH) added to increase speed of reaction
Why is KOH less common Carbon Dioxide Absorber?
KOH less common – implicated in reactions that produce carbon monoxide and compound A
How much heat and energy is released with Carbon Dioxide Absorption?
The overall exothermic carbon dioxide absorption reaction releases approximately 13,000 kcal of heat energy for every 22.2 liters (1 mole) of carbon dioxide absorbed
What temperatures within the soda lime can be reached with Carbon Dioxide Absorption?
Temperatures within soda lime can reach 45 to 50 degrees Centigrade
What is the average to maximum production of CO2 by anesthetized adult?
12-18 L/hr
What is the standard grandula size?
4 to 8 mesh is standard size for granules
Define four mesh granule.
A granule that will pass through a screen with four wires per linear inch
Define eight mesh granule.
A granule that will pass through a screen with eight wires per linear inch
What is true about the mesh number and the absorbent particle?
The higher the mesh number the smaller the absorbent particle
What is the property of large granules?
Larger granules have less resistance to flow but are less efficient secondary to smaller surface areas relative to their mass
What is added to effect the hardness and friability of granulas?
Inert silica and kieselguhr added to granules to increase hardness and decrease friability
What is present on each granula? What does it do?
Each granule has pitted pores to increase the surface area
What are the thre most important factors for absorbent granules?
- Size
- Porosity
- Nature of the granule surface
Review Carbon Dioxide Absorption: Granule Size.
Review Characteristics of Absorbents.
Table 16.5
What is the relationship of dust and Carbon Dioxide Absorption?
Dust (fines) from soda lime implicated in laryngospasm, bronchospasm and machine failure
What can all current carbon dioxide absorbents cause?
can cause irritation to mucus membranes
When does channeling occur?
Occurs in loosely packed canisters or when the canister design allows the gases to pass along the sides
What does gas take?
- Gas takes the path of least resistance
- Leads to exhaustion of granules exposed to gas flow
What needs to be done to prevent channeling?
Shake canister before installation into circle system
What indicated absorbent exhaustion?
Indicator dye is an acid or base that is added to the absorbent to signify absorbent exhaustion
What type of indicator dye is added to the carbon dioxide absorber to indicate exhaustion?
- Ethyl violet
- At a pH of 10.3 the ethyl violet changes from colorless to blue-purple
What can occur after exhaustion?
- No true regeneration
- Absorbent color reversion can occur after rest
What is the amount of reversion dependent on?
Amount of reversion dependent upon length of the rest period
Review clinical signs of carbon dioxide absorbent exhaustion.
Box 16.15
What do you do if granule exhaustion occurs during a case?
Steps to take for granule exhaustion during a case: increase FGF 1-2x MV & replace at end of the case
What does soda lime degrade?
Degrades most current volatile agents
What volatile agent is degraded the most?
sevoflurane
What volatile agent is degraded the least?
desflurane
What did the soda lime use to contain?
Historically contained a high amount of potassium and/or sodium hydroxide
What happens when soda lime is desiccated? (2)
- Exothermic degradation of inhalational agents
What can be produced by soda lime and sevoflurane?
Reaction with volatile anesthetic to form Compound A with sevoflurane
Sevoflurane _____ in soda lime
unstable
What does sevoflurance produce?
Produces compound A
What levels are compound A dangerous?
- Lethal at 130-340 ppm
- Produces renal injury at 25-50ppm in rats
What compound A levels are achievable in clinical practice?
Compound A concentrations of 25-50ppm are achievable in clinical practice
What can increase compound A levels?
Levels increase with increased absorber temperature, low flow rates, high sevoflurane concentrations, anesthetics of long duration, and absorbent dessication
What can help decrease the chance of compound A?
Product insert – Avoid fresh gas flows less than 1-2 L/min for more than 2 MAC hours
How is carbon monoxide formed?
Formed when desflurane*, enflurane or isoflurane pass through dry (dessicated) alkaline rich absorbents (e.g. potassium hydroxide, sodium hydroxide)
What can help decrease the chance of carbon monoxide formation (3)?
- Turn off oxygen at end of case
- Change absorbents regularly
- Use low flows to avoid drying
What do the bellows do?
Compressed gas (oxygen or air) serves as driving mechanism to compress bellows
What do ventilator relief valve maintains?
Ventilator relief valve (bellows pop off valve, spill valve, overflow valve) maintains circuit volume and pressure by releasing gas to the scavenger in the amount equal to the fresh gas flow per minute
When do bellows open?
Only opens during expiratory phase
What happens to inspiration to the driven bellows?
During inspiration driving gas closes the relief valve
What happens to the bellows when they open during expiration?
During expiration a weight in the relief valve holds the path to the scavenger closed until the bellows are filled
How much positive end expiratory pressure in the breathing circuit is generated with the bellows open?
Generates 2-3 cmH2O
What is the important difference between ascending/standing and descending/hanging bellows?
when there is a disconnection or a major leak the ascending/standing bellows will collapse
What happens when a disconnection occurs with descending/hanging bellows?
the ventilator will continue its up and down movements drawing in room air and driving gas during its descent and discharging it during the upward movement
How do you differientate between ascending/standing and descending/hanging bellows?
watching during expiration
What bellows rise during expiration?
Ascending bellows
What bellows descend during expiration?
descending bellows fall
What type of bellows are found in most AGM?
Most modern anesthesia machines have ascending bellows because they are thought to be safer
Where do ascending bellows attached?
Attached at the base of the assembly
What happens to the ascending bellows during inspiration?
Compress downward during inspiration
What happens to the ascending bellows during expiration?
During exhalation expand upward
Where do descneding bellows attach?
Attached at the top
What happens to the descending bellows during inspiration?
Compress upward during inspiration
What happens to the inside the descending bellows?
Inside the dependent portion of the bellows is a weight that facilitates re-expansion downward during exhalation
What do Piston Driven Ventilators use?
- Use electric motor to compress gas in a rigid piston during inspiration
- Use no driving gas
How is volume delivered in the piston ventilators?
Volume delivered by the piston is determined by the distance the piston moves
How do Piston Driven Ventilators work?
When a volume is set to be delivered the piston is moved the distance required to delivery the set volume to the patient
What are the advantages of piston driven versus bellows design?
- Quiet
- Precise tidal volume
- No PEEP
- Fewer compliance losses
- Electricity is driving force of the piston so if pipeline fails can continue without exhausting oxygen cylinder
- Capable of all modern ventilation modes
What are the disadvantages of piston driven versus bellows design?
- Not visible
- Quiet
- Cannot easily accommodate non-rebreathing circuits
- Potential for negative end-expiratory pressure and dilution of patient’s inspired gas with room air
Review the modes of ventilation.
- Volume controlled ventilation
- Pressure controlled ventilation
- Synchronized intermittent mandatory ventilation
- Pressure controlled ventilation with volume guarantee
- Pressure support ventilation
- Continuous positive airway pressure
- Bilevel positive airway pressure
- Positive end expiratory pressure
Review the scavenging system.
What is the scavenging system?
Collection of waste anesthetic gases from the breathing circuit and ventilator and their removal from the OR
What must be done to avoid barotrauma or failure to ventilate?
An amount equal to the FGF must be scavenged each minute to avoid barotrauma or failure to ventilate
What makes up the scavenging system? (5)
- Gas collecting assembly
- Transfer means
- Interface
- Disposal tubing
- Gas disposal assembly
Define gas collecting assembly.
Captures gases as the site of emission
Define Transfer means.
Conveys gases to the interface
Define interface.
Provides positive pressure or negative pressure relief and may provide reservoir capacity
Define disposal tubing.
Conducts gases from interface to gas disposal assembly
Define gas disposal assmebly.
Conveys gases to a point where they can be safely discharged
Review transfer means location on the AGM.
What is the most important part of the gas scavening unit?
Scavenging Interface
What does the Scavenging Interface serve?
to prevent pressure increases or decreases in the scavenging system from being transmitted to the breathing circuit, patient lungs, or ventilator
What are the different types of the scavenging interface?
Open versus closed
- Closed seen on older machines
- Closed useful where passive scavenging is used
- Hospital accreditors require active scavenging is U.S.
Where is the positive pressure relief valve located on the closed scavenging?
located on the interface
What is the purpose of the Positive pressure relief valve on the closed scavenging?
If the suction attached to scavenger fails or if a hose distal to it becomes kinked the positive pressure relief valve opens before pressure buildup within the scavenger is transmitted to the breathing circuit and the lungs
What can occur from excess positive pressure building up in the breathing system?
excess positive pressure build-up in breathing circuit –risk of barotrauma
Where is the waste dumped back into with the Positive pressure relief valve?
Waste gas dumped back into OR
Where is the Negative pressure relief valve located ?
on the interface for safe use with suction
What happens to the Negative pressure relief valve?
When suction is excessive the negative pressure relief valve opens to draw in room air
What does the negative pressure relief valve prevent?
Prevents emptying of gas from patient breathing circuit (could lead to excessive suction on the patient breathing circuit)
Review open scavenging system.
Where is the Open Scavenging System open to?
Open to the atmosphere; safer d/t less risk of positive/negative pressure being applied to breathing circuit
What does the Open Scavenging System rely on?
on open relief ports for positive and negative pressure relief
What are the characteristics of Open Scavenging System?
Each patient exhalation is led to the bottom of the open interface reservoir where a second tube withdraws it by suction before the next exhalation arrives
What is critical for proper functioning of Open Scavenging System?
Appropriate suction is critical to proper functioning
What can inadequate suction on the Open Scavenging System cause ?
Inadequate suction results in patient exhalations releasing waste gases into the OR
What happens to the needle on the open scavenging system?
When the needle valve of the open reservoir scavenger is adjusted properly, flowmeter (suction indicator) float falls between two lines on the flowmeter
Be able to id disposal tubing.
Be able to ID gas disposal assembly.
Who regulates waste gas exposure?
regulated by Occupational Safety and Health Administration (OSHA)
What is waste gas exposure based on?
Based on time-weighted 8 hour average concentration
What is the limit for waste gases?
Limit halogenated agents to 2 ppm or 0.5 ppm with nitrous oxide
What is the recommended waste gas exposure?
Workers should not be exposed to an eight hour time-weighted average of > 2 ppm halogenated agents (not > 0.5 ppm if nitrous oxide is in use) or > 25 ppm nitrous oxide when used alone
100% of a gas is _______ ppm
1,000,000
1% is _______ ppm
10,000
What is true about the smell of an agent and the population level?
If you can smell an agent, the pollution level approximately 5-300 ppm
What are variables that alter waste reduction? (4)
- Room ventilation
- Condition of anesthesia equipment
- Effectiveness of scavenger
- Anesthetic technique of the user
Review AGM Checklist.
Nagelhout - Boxes 16.22 and 16.23 (pp 267-271)
What is the principle behind the Draeger apollo?
Uses a piston ventilator
How is mechanical ventilation achieved with a draeger apollo?
Mechanical ventilator is activated in 2 steps: the mode is chosen, and then is confirmed by a second key press
What are the ventilation modes altered by the Draeger apollo?
Ventilation modes offered: manual, spontaneous, VCV, PCV, PSV, autoflow, SIMV mode
What is the checklist of the Draeger apollo?
Electronic checklist assists the user in preuse checkout
What is not included in the Draeger Fabius GS?
Patient monitors are not included – have to be added on
What is the battery of the Draeger Fabius GS?
45-minute battery reserve
What remains after the battery is exhausted as the Draeger Fabius GS?
- Pneumatic functions remain after the battery is exhausted:
- Uses manual checklist w/several electronic self-tests (system, leaks, compliance)
What is included in the GE Aisys?
- Includes physiologic monitors
What drives the bellows of the GE Aisys?
Oxygen-driven standing bellows
What ventilator modes are present in the GE Aisys?
Ventilation modes: manual, spontaneous, VCV, PCV, PCV-VG, PSV-Pro, CPAP/PSV, SIMV, & PSV
What is widely offered with the GE Aisys?
- Wide-range of tidal volumes offered
- Supports low-flow anesthesia
What cassettes are used with the GE Aisys?
Uses Aladin cassette vaporizers
What controls are present in the GE Aisys?
Electronic control, measurements, & display of fresh gas flow
What does the user select on the GE Aisys?
User selects desired carrier gas (nitrous oxide or air), total fresh gas flow, & inspired gas concentration
What is not present on the GE Aisys?
No needle valves or glass flowmeter tubes
What is needed as a backup on the GE Aisys?
Backup needle valve & glass flowmeter tube
What will not be delievered in the GE Aisys?
Will not deliver volatile agent or nitrous oxide w/o main power or battery backup & adequate oxygen pressure
What is the prinicple of GE Aestiva?
Has traditional mechanical/pneumatic systems w/ a modern & capable ventilator
What ventilator modes are present on GE Aestiva?
Uses oxygen-driven standing bellows capable of: manual, spontaneous, VCV, PCV, PSV-Pro, & SIMV
What switch is present on the GE Aestiva?
1-step “bag/vent” switch
What is the checkoff procedure of GE Aestiva?
Mostly manual checkout procedure
What is true about the fresh gas flow and GE Aestiva?
No electronic capture of fresh gas flow
What oxygen sensor is used in the GE Aestiva?
Uses galvanic fuel cell type oxygen sensor
What is the backup power for GE Aestiva?
30-min battery reserve w/fresh gas, vaporizers, & ventilator
What is the properties of GE Aespire?
Similar to Aestiva but more compact
What modes are offered by the GE Aespire?
Offers volume control & pressure control modes of ventilation
What is the GE Avance similar to?
Similar to Aisys
What is the properties of the fresh gas flows of the GE Avance?
Has electronic fresh gas flow controls w/backup pneumatic control
What ventilator modes are available on the GE Avance?
Modern multimode ventilator, spirometry, integrated physiologic monitoring
What is different about the GE Avance?
Tec 6 & Tec 7 vaporizers different from Aisys
What ventilation is available on the Mindray?
Offers multiple ventilation modes
What does the Mindray offer?
Offers automatic preanesthesia machine checkout
Id this ventilator.
Penlon
What are the components of the Draeger Narkomed?
- Older AGM
- May still be used in some ASC and office-based practices
